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Polyol-Mediated Synthesis and Electrochemical Characterization of Nanostructured LiMn2O4 and LiNi0.5Mn1.5O4 Cathodes LiMn2O4 (LMO) and LiNi0.5Mn1.5O4 (LNMO) spinels have been extensively studied as promising cathode materials for high voltage Li-ion batteries. Their electrochemical performance has been revealed to be significantly influenced by their crystallographic structure as well as the particle size and morphology, which are strongly dependent on the synthetic methods. Conventionally, LMO and LNMO spinels are prepared via solid-state reactions, which offer limited control over the particle size and morphology of the final product. As an alternative, the polyol method has been demonstrated as a versatile method for the preparation of highly crystalline nanoparticles with well-defined particle size and morphology. The synthesis of LMO materials via polyol method has been only reported by the group of Gerand et al., while the preparation of LNMO via polyol method has not been published so far. Therefore, this work focuses on the further development of the polyol method for the preparation of LMO and LNMO materials. The influence of the synthesis conditions on the electrochemical performance of the as-prepared materials is systematically investigated. Nanostructured LMO and LNMO materials were successfully obtained via polyol method followed by calcination in air. An additional ball milling process before calcination optimized the particle morphology of the materials and thus lead to remarkably enhanced electrochemical performance. Furthermore, the calcination temperature was revealed to influence the electrochemical performance of the materials as well. For LMO materials, the ball milled sample with successive calcination at 700 °C exhibited the optimized electrochemical performance. It showed excellent cycling stability (97.9 % capacity retention after 100 cycles) and advanced rate capability (81.9 % capacity retention at 20C). For the LNMO materials, on the contrary, a calcination temperature of 800 °C was required to ensure low degree of Ni/Mn cation ordering. The ball milled LNMO sample with successive calcination at 800 °C retained 94.8 % of its initial discharge capacity after 100 cycles and offered 83.8 % capacity retention at 20C. These LMO and LNMO materials are potentially promising as highvoltage cathode materials for Li-ion batteries.

rwth publications (rwth aachen)

Polyol-vermittelte Synthese und elektrochemische Charakterisierung von nanostrukturierten LiMn$_{2}$O$_{4}$- und LiNi$_{0,5}$Mn$_{1,5}$O$_{4}$-Kathoden